ALMATY, Kazakhstan -- Jailed Kazakh dissident poet Aron Atabek, who has been behind bars since 2007, has been hospitalized for unknown reasons amid a series of reports that the 68-year-old's health is failing.

Yelena Semyonova, a human rights activist in the northern city of Pavlodar, told RFE/RL on September 28 that she learned a day earlier from prison authorities at the AP-162/1 correctional facility that Atabek had been rushed to the hospital several days earlier.

"He is being fully examined and is receiving vitamins now. After a full set of examinations and tests, the diagnosis will be made and treatment will be determined," Semyonova said, adding that she has no detailed information on Atabek's health situation.

Neither medical personnel at the hospital nor officials of the State Penitentiary Service would comment on Atabek’s condition.

Officials at the AP-162/1 correctional facility told RFE/RL that they will provide information on the situation only after questions regarding Atabek's case are submitted in written form.

Atabek's hospitalization comes as a petition signed by more than 2,500 people was sent to President Qasym-Zhomart Toqaev, urging him to release Atabek due to his deteriorating health.

The poet, who was sentenced to 18 years in prison after being convicted of helping organize protests that resulted in the death of a police officer, is said to be suffering from heart disease, diabetes, and arthritis.

Atabek has maintained his innocence. He rejected a 2012 government pardon offer that would have required him to admit guilt.

Kazakh authorities have shown little, if any, tolerance toward criticism, whether it comes from the independent press, activists, or political opponents.

Human rights groups in Kazakhstan have said that Atabek has been constantly tortured in prison, with guards intentionally splashing water with high concentrations of chlorine on the floor of his cell to damage his health.

For years domestic and international rights organizations have demanded the Kazakh government release Atabek.

Last month, a picture of Atabek, taken by human rights activists who visited the dissident poet in prison, caused a public outcry. The poet looked extremely exhausted, sick, and in poor shape.

Atabek was transferred to solitary confinement in December 2012 and spent two years there after an article he wrote critical of then President Nursultan Nazarbaev and his government was smuggled out of prison and published online.

Atabek and his relatives said in 2014 that prison guards had broken his leg, which the authorities denied.